Freeze–Thaw and Carbonation Resistance Performance of All-Lightweight Shale Ceramsite Concrete

To investigate the durability of all-lightweight shale ceramsite concrete (ALSCC), specimens of ALSCC20–ALSCC45 with compressive strengths ranging from C20 to C45 were prepared. A comprehensive analysis of the frost resistance of ALSCC was conducted based on appearance, relative mass, compressive strength, and relative dynamic elastic modulus. Additionally, the depth of carbonation was examined, and the carbonation resistance was evaluated. The results indicated that the frost resistance and carbonation resistance of ceramsite concrete improved with higher-strength grades. After 200 freeze–thaw cycles, the mass loss, relative dynamic elastic modulus loss, and compressive strength loss of ALSCC45 were 32.7%, 70.6%, and 39.9% of those of ALSCC20, respectively. After 28 days of carbonation, the carbonation depth of ALSCC45 was only 43.9% of that of ALSCC20. Compared to ordinary concrete, ceramsite concrete demonstrated superior frost resistance due to its thermal insulation properties, “self-curing” effect, and the formation of numerous hydration products that enhanced the internal structure of the concrete. Additionally, compared to ordinary concrete, ALSCC exhibited superior carbonation resistance due to the porous and highly absorbent nature of ceramsite, which absorbed a significant amount of water and CO2, thus slowing the rate of carbonation. Additionally, this study developed a freeze–thaw damage model based on the functional relationship between the relative dynamic modulus of elasticity of ALSCC and the number of freeze–thaw cycles as well as a carbonation depth prediction model based on ALSCC carbonation test data, compressive strength, and water–cement ratio. These models effectively capture the freeze–thaw damage patterns and carbonation behavior of lightweight aggregate concrete across different strength grades.